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This invention relates to flowmeter and more particularly to electromagnetic flowmeter measurement of either magnetic or non-magnetic, compressible or incompressible fluid flow in a steady or transient fluid state, when fluid flow is characterized as single-phase or multi-phase, including combinations of gases, liquids, vapors, particles, and/or emulsions, and when fluid flow is either forward or backward through a flowmeter, so that obstructionless fluid flow measurements can be made.
Fluid flowmeter for many applications already exist. Flowmeter are devices that measure the rate of flow or the quantity of a moving fluid in an open or a closed conduit. They are characterized as consisting of a primary device and a secondary device. The primary device is mounted internally or externally to a fluid conduit. A primary device produces a signal generated by the interaction of the fluid with the physical configurations or manifestations of the device. The secondary device responds to the signal from the primary device and converts that signal into a display or other presentation to indicate flow rate. Flowmeter are fabricated from various materials and constructed in different configurations. Both the primary and secondary devices use a variety of physical means to identify the flow rate of a fluid through a conduit.
Several variables determine how a fluid flowmeter is constructed and used. These variables include, type of fluid; temperature and pressure limits, steady-state, pulsating, or transient fluid flow, range of flow measurement, pipe size; flow conditioner size; length of meter runs to generate stable flow before measurement; surface roughness; number of blades internal to a turbine flowmeter; friction forces; springs; pistons; floats; and other mechanical configurations, such as cones; tubes; and targets. In addition to these variables affecting fluid flowmeter construction and application, costs related to installation and to fluid-flow pressure drop across the meter must be considered. A pressure drop across the meter requires more pumping energy and therefore generates higher fluid pumping costs, especially in large diameter conduits.
There are fluid flow obstruction problems associated with flowmeter applications. These obstruction problems include poorly configured conduit systems, fittings, and other physical devices that may generate an obstruction in the path of a moving fluid. Within the existing range of technologies for fluid flow measurement, most obstructions adversely affect fluid measurement even while generating primary device signals. All obstructions generate a pressure drop within the fluid system.
Fluid flowmeter are also classified as differential producers or linear scale meters. Differential producers include orifice meters, target meters, venturi meters, flow nozzles, low-loss meters, pitot tube meters, and elbows. Linear scale meters include magnetic flowmeter, positive displacement meters, turbine meters, ultrasonic meters, variable area meters, and vortex meters.
The few fluid flow measuring technologies that do not use obstructions include ultrasonic signal and electromagnetic field signal evaluation. Ultrasonic flowmeter that use ultrasonic transmitters and receivers are placed externally to a conduit to sense the change in time of transmitted and received ultrasonic signals within a fluid. The variation in time for the transmitted and reflected signals is translated into fluid flow rate. Doppler flowmeters, another type of ultrasonic flowmeter, reflect the flowing fluid pressure front to a detector by particulate matter in the fluid. The difference in a doppler meters"" reflected frequency and fixed frequency is related to the flowing fluid rate. Obstructionless flowmeters also include electromagnetic fluid flowmeters that are based upon the principle of electromagnetic induction. These flowmeters average the velocity of the fluid over the conduit area. Measured fluids must have adequate magnetic properties so that the fluid will support an electromagnetic field.
The measurement of compressible fluids over short time periods when the fluid is in a transient state is an extraordinarily complex problem that is not specifically addressed by existing flowmeter technologies. As a result, both historically and practically, fluid dynamic measurements concentrate on steady-state flow rates where averages of the fluid flow are determined. Instantaneous fluid flow measurements are not often made due to the wide variety of disturbances that can affect the fluid flow rate and due to slow time constants in conventional flowmeters. For example, in most industrial applications, pulsation and transient behavior are considered to be undesirable flowing fluid properties. Pulsation dampeners are often used in fluid systems to decrease pulsation effects and fluid capacitances and fluid accumulators are used to further reduce transient fluid flow behavior. Thus, the measurement of fast-transient fluid flow, and correspondingly, steady-state fluid flow are not dual design parameters in current flowmeters. As a result, current technology is directed to flowmeters that measure average, continuous, steady-state flow rates.
Swirling flow is a common deleterious effect in gas flow measurements. Swirling is caused by elbow fittings out of plane in pipelines. Swirling creates additional measurement problems for common flowmeters such as orifice plate, turbine, and vortex meters, which require relatively undisturbed flow profiles to generate reproducible, reliable, and accurate measurements. Improvement in the measurement of swirling gas flow rates has been reported for the v-cone flowmeter. The v-cone meter is an obstruction, differential pressure, flowmeter in which a cone is placed in the fluid flow path.
The patent literature includes the description of a number of fluid flow measuring devices that address mechanical motion associated with magnetic followers to indicate the conditions of fluid flow. Among the patents is U.S. Pat. No. 3,805,611 to H. A. Hedland (1974) that teaches a single magnetic piston, a conical interior unit to modify fluid flow rate, and a magnetic follower, exterior but concentric and contiguous to the flowmeter housing, to track the mechanical position of the internal magnetic piston and to show flow rate on a mechanical scale. U.S. Pat. No. 3,805,611 represents a beneficial fluid flowmeter with a number of practical advantages. However, the Art taught in U.S. Pat. No. 3,805,611 suggests that fluid flow is not impeded by internal components in the path of a flowing fluid. This description contradicts the known laws of physical science, which require a pressure drop across any passive annular fluid device through which fluid flows. However, this minor discrepancy in description does not affect the practical application of Hedland""s flowmeter that has been used in many flow measurement environments in the petroleum industry.
The issue of pressure drop associated with flow rate measurement is an important issue that affects the manner in which flowmeters operate. Pressure drop across a fluid flow rate measuring element is especially important when considering explosive, instantaneous, transient, or fast periodic fluid flow rate measurement.
As a result of the focus of prior Art on steady-state fluid flow measurements, current methods to acquire fluid flow rate data for explosive, fast, non-steady-state, moving fluids suffer a number of disadvantages when addressing fluid flow rate variation, including the disadvantages listed below.
[1] Prior Art in measurement of fluid flow rate focuses upon thermodynamic steady-state conditions of flow and does not specifically address transient and other non-steady-state conditions as the primary focus of fluid flow measurement.
[2] Because existing flowmeters do not focus on explosive, transient, and fast non-steady-state fluid flow measurement, their accuracy and precision are compromised.
[3] Existing obstructionless flowmeters, such as ultrasonic flowmeters, require added installation space around the fluid conduits.
[4] Primary device design in conventional flowmeters that use mechanical components permits measurement of fluid flow in only one direction.
[5] Inertia associated with flowmeters having mechanical blades generates long time constants when such devices measure flow rate, and thus prevents these flowmeters from measuring short duration fluid flow rates accurately.
[6] Because existing flow measuring technology focuses upon steady-state fluid flow, piping systems require flow conditioners and/or long pipe runs to generate suitable conditions for flow measurement.
[7] Current flow measuring technology is an averaging technology that focuses upon averaging flow before measurements are taken rather than after measurements are taken.
[8] Current flow measuring technologies that use a magnetic field response require, either a fluid that will support a magnetic field as the measured medium, or a magnetized component and magnetic follower to generate a primary response for flow rate.
[9] Current flow measuring technologies that generate a pressure drop across the measuring device, such as orifice meters, v-cone meters, critical flow nozzle meters, and venturi meters, measure flow rate with a restricting flow geometry that reduces the area of a flow orifice in order to generate a pressure difference related to fluid flow rate.
[10] There are no broadly applicable flowmeters that use electromagnetic field strength variation to measure the flow rate of non-magnetic-field-supporting fluids.
[11] No methods are available to check calibration, to recalibrate, or to validate operation of flowmeter primary and/or secondary devices in field installations without using either a flowing fluid for calibration and/or removing the flowmeter for bench-calibration.
[12] Existing flowmeter technology uses an electrical, an electronic, or a mechanical method for calibration and does not provide for an approach in which amplitude and frequency of an electronic signal and the mechanical position of an electrical coil or coils are combined for calibration purposes.
[13] Existing flowmeters are not based upon a resonant electronic circuit.
[14] The time constant of a conventional flowmeters is not usually specified because fluid flow rate measurements are conducted in steady-state environments.
[15] The expansion of fluid is not a principal focus for measureing fluid flow.
[16] Existing flowmeters for multi-phase fluids do not use fluid expansion and contraction chambers and obstructionless geometry to produce a primary signal that is generated from a change in density of a multi-phase fluid.
In accordance with the principles of the disclosed invention, defined as, Annular Void Electromagnetic Flowmeter [AVEF], the characteristics of operation that distinguish this invention from prior Art are described below.
(a) An electromagnetic field measurement upon which fluid flow is based permits the physical, internal, components of the AVEF to be used with standard pipe components when such components are appropriately modified.
(b) There may be no fluid flow obstructions introduced into the fluid system by the measuring device. The absence of obstructions dictates that a threshold of fluid flow exists before the AVEF will respond to fluid flow. The minimum response of my AVEF is therefore dependent upon the amount of flowing fluid, the physical properties of the fluid, the physical configuration of the flowmeter, and the physical properties of the components within the flowmeter.
(c) Transient or steady-state fluid flow measurements are determined by the same physical configuration. In transient fluid flow measurements, the time constant of my AVEF is on the order of magnitude of 10xe2x88x923 seconds (0.001 seconds) which permits measurement of rapidly expanding and rapidly compressing fluids through the flowmeter.
(d) Measurement of fluid flow rates by my AVEF depends upon changing an electromagnetic field but does not require a fluid that supports a magnetic field.
(e) My AVEF includes one or more pistons fabricated from ferromagnetic material or other material that supports a magnetic field, with a void through the piston(s), which void may be smaller than, equal to, or greater than the diameter of the fluid system conduit. The void may be any shape sufficient to permit fluid flow through the piston(s). When such void is at least equivalent to the void though the related conduit system that is used to convey the flowing fluid, the piston(s) produce obstructionless flow. The preferred embodiment of the void is an area of the same size as the conduit though which the fluid is flowing.
(f) My AVEF includes a means to reposition piston(s) moved by fluid flow. When fluid flow changes, the piston(s) may be repositioned to a greater or lesser flow-rate position or to a zero flow-rate position, depending upon the fluid flow force on the face of the piston(s).
(g) My AVEF includes a housing for the piston(s) and for the means to reposition piston(s). A non-magnetic material is preferred for the repositioning means.
(h) My AVEF contains one or more electrical coils positioned externally to the housing, either axially around the housing at a right angle to the internal piston(s), or bent into a longitudinal or oval shape placed parallel to the piston(s) and contiguous to the housing, with the coil(s) having the capability to sense a change in electric current impressed on the coil(s) when a piston that supports a magnetic field moves toward or away from the coil(s). When a coil is positioned axially with respect to the housing, when the inside diameter of the coil and external diameter of the housing are the same, the coil is next to the housing. If the inside diameter of the coil is larger than the outside diameter of the housing, the coil is placed away from the housing. In either case, the magnetic field generated by the coil will be altered by the movement of a piston made from material that will support a magnetic field, which movement changes the impedance of the coil and, correspondingly, the current associated with the electromagnetic field.
(i) My AVEF includes a metal shield-cover that encloses the coil(s) and the housing, described in (h) above. The cover shields internal components from external electromagnetic fields, and contains the internal electromagnetic field generated by the coil(s).
(j) My AVEF primary device includes a housing, a piston or pistons, and a means to reposition the piston(s) in the housing.
(k) In a two-piston configuration of the primary device, the zero point of one piston may be placed at one end of the housing with the zero point of the other piston placed at the other end. In this configuration, fluid can enter the flowmeter from either end of the housing. A single repositioning means acts upon the two pistons simultaneously; a double repositioning means acts upon each piston separately.
(l) My AVEF secondary device includes coil(s); electronic components needed to generate an electronic signal impressed upon the coil(s), amplification and noise control circuits to detect modified electric current in the coil(s) from piston motion; and a display of the voltage generated, calibrated to reflect fluid flow through the flowmeter.
(m) The flowmeter secondary device includes a means to change the amplitude and frequency of the signal impressed upon the coil(s) to fix a resonant, or near resonant, operating point for detecting fluid flow rate.
(n) Fluid flow rate can be calibrated to reflect either a positive or negative response to the motion of the piston(s). With certain electronic circuit settings of the secondary device, and placement of the coil(s) with respect to the piston(s) of the primary device, positive or negative responses can be obtained. By design, a relative zero can be set at a specific flow rate, so that a positive response is generated in one direction and a negative response is generated in the opposite direction from the relative zero. The preferred response is positive for a positive piston displacement toward the coil(s).
(o) With certain geometrical configurations of the flowmeter coil(s) and housing, when a ferromagnetic material is placed next to a coil, the flowmeter response of the secondary device can be verified by moving the ferromagnetic material.
(p) The linear position of the flowmeter coil(s) on the flowmeter piston housing can be adjusted for sensitivity and calibration from outside the shield-cover. This permits adjustment of the coil(s) without removing the cover.
(q) The strength and polarity of the signal obtained from movement of the piston(s) depend upon the position of the coil(s) relative to the piston(s) and upon the impressed frequency on the coil(s) relative to the resonance frequency of the resonant circuit.
(r) At each end of the flowmeter housing, end-fittings ensure pressure integrity of the housing and provide a stop for each end-piston inside the housing. Each end of the housing also includes a fluid expansion or contraction chamber (e/c chamber) that is conical or cylindrical in shape. Depending upon flowmeter design, an e/c chamber may be in the housing or in the end-fitting. When upstream fluid reaches a first e/c chamber, fluid expands and density decreases momentarily, generating force on an upstream piston frontal area. Upon leaving the housing, fluid encounters a second e/c chamber wherein the fluid undergoes contraction and the original fluid density is recovered. When a steady-state fluid flow pushes on the frontal area of the piston, the piston will achieve a position of equilibrium created by the force of the fluid on the piston and the opposing force of the restoring means. The preferred means for repositioning the piston is a spring of appropriate length, diameter, stiffness, and non-magnetic material. When fluid flow is in a transient state, the piston will move from one equilibrium position to another, depending upon the initial and final flow rates that create the transient flow. If the initial and the final flow rates are zero, transient flow will cause a piston to move away from and return to zero. If a transient state is short, the piston will move in a pulse manner. If a change in state is sufficiently long, the piston will move to an equilibrium position, and steady-state flow rate can be measured between periods of transient flow.
A certain threshold level of fluid flow through my AVEF must be achieved before the fluid will expand with sufficient force to move piston(s). The threshold level of fluid flow generates a corresponding threshold of detection of the flow. This threshold of detection depends upon a number of physical variables, including: (i) force generated by the flowing fluid; (ii) pressure associated with the flowing fluid; (iii) geometry of the flowmeter housing; (iv) geometry and mass of the piston; (v) friction forces associated with the sliding piston in the housing; (vi) damping associated with piston movement; (vii) fluid compressibility; (viii) fluid density; (ix) e/c chamber dimensions; and, (x) force generated by a restoring means. For example, with all variables except the piston repositioning spring held constant, different spring constants create correspondingly different thresholds of detection of fluid flow for the same fluid, flowmeter housing, piston(s), and e/c chambers.
The electromagnetic field generated by the coil(s) is altered by piston movement. This electromagnetic field exists both externally and internally to the flowmeter housing. The movement of a ferromagnetic piston alters the strength of this field and changes the impedance of the resonant coil-capacitor circuit. A given displacement of a non-magnetized piston generates a steady-state response that can be used to measure fluid flow rate. For the same piston displacement, a magnetized piston generates a transient response that cannot be used to measure fluid flow rate.
It is therefore to be understood that the objects of the present invention are
[1] to provide an apparatus to measure fluid flow rate with no obstructions in the fluid path so that only customary pressure drops in a fluid system of conduits and components are present, thereby eliminating back pressure and using a lower amount of energy to move the fluid;
[2] to provide an apparatus to measure fluid flow rate when the rate is explosive, transient, and/or of very short time duration, as well as to measure fluid flow rate when the rate is in steady state, thereby permitting transient rates to be compared to steady-state rates through the same fluid system using the same measuring apparatus;
[3] to provide an apparatus to measure fluid flow rate under minimum energy input conditions, such that the apparatus can measure rates at low capacities and high pressures, at low capacities and low pressures, at high capacities and high pressures, and at high capacities and low pressures;
[4] to provide an apparatus to measure fluid flow rate in equipment wherein there is insufficient room to include flow-conditioners and/or long conduits upstream and downstream of a measuring device, thereby providing a means to measure fluid flow rates in places where such measurement is difficult;
[5] to provide an apparatus that contains a minimum number of parts to maximize the reliability and minimize the cost of the apparatus;
[6] to provide a mechanical means to verify the operation of the AVEF and to validate the electronic calibration of the apparatus in the field, without having to shut down the fluid system to remove the AVEF for calibration and without requiring technical expertise in setting electronic calibration gains; and,
[7] to provide a flowmeter that can be calibrated with respect to density of multiphase fluids when such multiphase fluids cause a piston to move differentially with respect to fluid density and fluid pressure.
In a preferred embodiment, my AVEF has a metal shield-cover. The apparatus has a pressure and fluid containment housing constructed of non-magnetic material containing non-magnetized piston(s) and non-magnetic repositioning spring(s). Fluid force on a piston face pushes a piston against the spring. With a lesser fluid force on a piston face, a piston is pushed back by the spring. When fluid force on a piston face is absent, the spring places the piston at a zero flow rate position. Fluid force is distributed on a piston face by an e/c chamber that can be any shape sufficient to allow fluid to expand against the frontal area of the piston.
A piston void can have the same dimensions as the fluid conduit to permit obstructionless fluid flow and thereby eliminate or significantly reduce back pressure. Fluid expansion in an e/c chamber permits a flowing fluid to impact a larger area of a piston face than the fluid would impact in the absence of this chamber. Thus, the e/c chamber permits the dimensions of a piston void to be the same as the dimensions of the conduit. If there is no e/c chamber, in order for a piston to move, the piston void must have a cross-sectional area smaller than the area of the conduit; this design obstructs fluid flow and generates back pressure.
A piston is constructed of ferromagnetic or paramagnetic material. One or more coils are placed axially or parallel to the direction of piston travel. An electrical signal is impressed on the coil(s) located exterior to the non-magnetic housing, so that a piston moving inside the housing causes a change in the magnetic lines of flux associated with the magnetic field generated by the coil(s). The change in magnetic flux caused by a moving piston becomes a constant when the piston moves from one position to another and, thereafter, does not move. A periodic fluid force on the face of a piston will move the piston back and forth, causing either an increase and decrease, or a decrease and increase, of magnetic flux. The electrical signal impressed upon the coil will respond similarly. The electrical signal will be represented by either a change in voltage amplitude or a change in current amplitude.
Voltage or current amplitude changes generated by a moving piston provide a response that is dependent upon the amplitude and frequency of the electrical signal imposed upon the coil(s) and upon the position of the coil(s) relative to the piston(s). In the preferred case of selecting voltage amplitude change as the method to identify fluid flow rate, a reference frequency is chosen in the region of the resonant frequency of the resonant circuit. A moving piston causes a change in the voltage amplitude of this reference frequency. Depending upon which side of the resonant frequency a reference frequency is chosen, and upon how coils arc placed with respect to pistons, the voltage amplitude from piston motion will either increase or decrease with respect to the reference frequency, voltage amplitude. Thus, for voltage amplitude changes associated with a given direction of piston motion, the direction and amount of change of the voltage are functions of the reference frequency, the resonance frequency, the resonant peak voltage amplitude, the inductance in the resonant circuit, the capacitance in the resonant circuit, the proximity or distance of the coil(s) to the piston, the orientation of the coil(s), and the type of metal used in the housing.
The preferred embodiment includes a coil of wire with resistance in the range of 600 to 2500 ohms, a reference frequency less than 4000 hertz, a reference voltage amplitude that is 90 percent of the maximum resonant voltage amplitude, and a metal shield-cover installed over the piston housing and coil(s), so that the coil and housing are shielded. The latter geometry permits the coil(s) to be moved in linear relation to the direction of piston(s) motion. The voltage amplitude may therefore increase or decrease depending upon whether a piston is moving out of or into an electromagnetic field when the piston is moving in only one direction. Non-magnetized ferromagnetic and paramagnetic materials will generate these results. In the voltage amplitude mode of operation, only non-magnetized materials will provide a constant voltage amplitude for a constant position of a flowmeter piston.
The preferred embodiment of the AVEF uses non-magnetic stainless steel [ss] (ss 304 or ss 316) for the housing, a metal or a composit metarial for the coil shield-steel cover, and stainless steel (ss 417) for the piston(s). Other materials that upport a magnetic field can also be used for the piston(s) such as non-magnetized iron or composite materials. In one embodiment, the flowmeter housing is constructed from a six-inch section standard stainless steel pipe. Appropriate end connectors or fittings secure the flowmeter piston(s) and provide pressure integrity.
Further objects and advantages will become apparent from consideration of the following descriptions and drawings.